Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990apj...356..646n&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 356, June 20, 1990, p. 646-661.
Astronomy and Astrophysics
Astrophysics
43
D Lines, Pre-Main Sequence Stars, Resonance Lines, Sodium, Stellar Winds, T Tauri Stars, Metal Ions, Optical Thickness, Stellar Mass Ejection
Scientific paper
Model calculations of the sodium ionization and excitation conditions in winds from T Tauri stars are reported. Line profiles for the sodium D doublet resonance lines are computed and compared to the observations. It is found that, in order to reproduce the observed features, the line optical depth, which is proportional to the neutral sodium column density in the wind, must be restricted to a narrow range (0.3 less than tau less than 3 for the blue component of the doublet). Tau is a strong function of the mass-loss rate M, but it is rather insensitive to the wind temperature Tg. By using both the values of tau inferred from the observed Na line profiles for a given object and the observed luminosity of hydrogen recombination lines, it is possible to obtain with good accuracy both Tg and M. The possible influence of different wind acceleration laws, of fast turbulent motions, of different stellar radiation fields (including photospheric lines), and of circumstellar disks are discussed. The method proposed to measure Tg and M turns out to be rather robust and insensitive to a variety of effects. The application to a restricted sample of T Tauri stars indicates Tg between 6000 K and 6500 K and mass-loss rates between 3 x 10 to the -8th and 3 x 10 to the -7th solar mass/yr. The winds are mostly neutral, and the mass-loss rates are in excellent agreement with those required to drive the associated CO outflows with a momentum-conserving shock.
Giovanardi Carlo
Natta Antonella
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